Freestanding Thermoelectric Energy Conversion Device

Abstract

A thermal to electrical energy conversion device has freestanding thin or thick films of thermoelectric materials, n or p type or both, extending from thermally conducting and electrically insulating substrates. The freestanding thermoelectric elements exploit up to two orders of magnitude higher free convective heat transfer coefficient and thermal resistance. The combined effect is very large temperature differential not possible with prior art unless an auxiliary cooling mechanism (pumped liquid or fanned air) is used. The large temperature differential results in higher efficiency and power output. Methods of making these thermal electric conversion devices are also disclosed.

Description

STATEMENT OF GOVERNMENT LICENSE RIGHTS[0001]This invention was made with government support under Grant Nos. ECCS 1028521 and IIP-1417173, awarded by the National Science Foundation, USA. The Government has certain rights in the invention.FIELD OF THE INVENTION[0002]The present disclosure is directed towards devices that increase the efficiency of Thermo-electric Energy (“TE”) Conversion in which waste heat is converted to electricity.BACKGROUND OF THE INVENTION[0003]The total amount of heat energy wasted in the United States is about 60-70 quadrillion BTU / year, equivalent to a loss of $6 billion per year. Harvesting even 20% of that waste heat would be comparable to adding 10-30 nuclear power plants. Thermo-electric energy conversion is a green (zero emission, operation and maintenance) technology to harvest electricity from waste heat. However, the conversion efficiency is often less than 10%, and to be commercially sustainable, this has to be improved to 30-40%, which is the effi...

AI Technical Summary

Benefits of technology

[0013]Where, ρ, A and l are resistivity, cross-section area and length of the thermoelectric legs. Another unique feature of the present invention is that miniaturization can be exploited to manufacture the freestanding thin / thick film thermoelectric devices in the same way as microelectronic devices. Miniaturization, as shown later, allows the thermoelectric elements to be assembled as both series and parallel configurations. While the prior art always embodies thermoelectric elements connected in series to increase the output voltage, our design allows their parallel combination as well to reduce the total internal resistance for applications where low resistances are required. Since a single thermoelectric element acts as a voltage source, parallel configuration can be used to reduce the electrical resistance. In such design, a set on thermoelectric elements are connected as parallel (inset of FIG. 7a), while such sets are added in series. This unique aspect allows our products to control the total internal resistance of the product.

[0014]It is important to note that a major class of devices in the prior art involve thin or thick film thermoelectric elements. However, these films are laid out on solid supports (or substrates). Since these thermoelectric elements are not freestanding but rather attached to a substrate, they essentially have the same temperature as the substrate. This is because their very small thermal masses are insignificant, compared to the very large thermal mass of the substrate. This causes very small temperature differential, which can be shown easily experimentally and theoretically.

[0015]It is also important to note that the present invention improves thermoelectric energy conversion efficiency and power output through unique design, even with existing materials such as bismuth telluride. The present invention will produce even better results with new materials innovation (with higher ZT) as they become available in the future for technological implementation.

[0019]The metal plates and metal pads preferably are copper. The n-type leg is preferably bismuth telluride and the p-type leg is preferably antimony telluride for low temperature range applications. For higher temperature ranges, lead telluride or silicon-germanium can be used. A significant advantage of this invention is that existing materials can be used to enhance efficiency. The insulators are preferably silicon nitride. If desired, a silicon substrate may be provided between the insulators and the hot structure.

Problems solved by technology

It is important to note that some of the prior art products do contain thin or thick film based designs, but these elements are not freestanding.

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